But Dr. Edward Brunner, an emeritus professor of anesthesia at Northwestern University Medical School in Chicago, said the information is critical. Dr. Brunner, who is a death penalty opponent, said injection can be painful, but it depends on the dosage and the training of those who administer it.

"The drugs, if not given properly, can cause a precipitate - like a solid gel - which will block the needle and not allow the flow of the medication. If the drug doses are not proper, the drug used to put the patient to sleep can wear off and the drug used to paralyze you can act, and the patient can be fully sensitive.

"The final drug is potassium chloride, which stops the heart. It is very caustic and burning if it is administered when the person is awake. It would be very devastating and painful," said Dr. Brunner, 74.